The present invention relates generally to radiation imaging systems, and in particular to radiation imaging systems which are designed to perform single photon emission computed tomography (SPECT) and especially adapted to perform positron emission tomography (PET).
Gamma (or Anger) cameras of the type disclosed in U.S. Pat. No. 3,011,057 (the entire content of which is expressly incorporated hereinto by reference), have been used extensively in nuclear medicine diagnostic imaging systems. Specifically, gamma cameras are typically employed in conjunction with a collimator to selectively filter the passage of emitted radiation of a radionuclide administered to a patient to the camera. A scintillating crystal associated with the gamma camera positioned behind the collimator emits visible light when struck by radiation. This visible light is then detected by transducers, such as photomultipliers and translated into electrical signals which can be processed in a known manner to obtain a visual image of the radionuclide distribution within the patient. In this manner, noninvasive visual imaging of a patient""s organs may be obtained and used by a physician to diagnose disease.
Gamma cameras employed in conventional SPECT imaging systems, such as those described in U.S. Pat. No. 5,554,848 (the entire content of which is expressly incorporated hereinto by reference) can be modified to perform coincidence imaging (i.e., conventional positron emission tomography (PET)) by removal of the collimators and addition of electronics to detect and record simultaneous events in both cameras.
While radiation point and line sources have been employed in the past in PET imaging systems to improve image quality (e.g., see U.S. Pat. No. 4,637,040, the entire content of which is expressly incorporated hereinto by reference), such conventional point and line source techniques do not operate well when employed in conjunction with gamma cameras associated with SPECT imaging systems when used in a coincidence imaging mode.
What has been needed, therefore is a transmission scanning technique which enhances the image quality of radiation imaging systems, and particularly single photon emission computer tomography systems operating in a coincidence imaging mode. It is toward fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in systems and methods which allow for patient-dependent attenuation maps to be measured for purposes of correcting attenuation effects in gamma camera coincidence imaging. In particularly preferred forms, the present invention is embodied in gamma-camera coincidence (GCC) imaging systems and methods which include a fixed-position point source of radiation energy.
Specifically, the preferred GCC imaging systems and methods of this invention include a pair of gamma camera imaging heads rotatable about a patient-longitudinal imaging axis. The imaging heads will each have a plurality of radiation opaque septa plates extending transversely relative to the imaging axis about which they locate. Such septa are used for emission imaging to filter out radiation originating from outside the scanner field of view. Adjacent ones of the septa plates are spaced apart along said imaging axis. At least one point source of radiation will thus be positionally fixed between a predetermined adjacent pair of the septa plates of one of the imaging heads so as to be concurrently rotatable therewith.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.